Assessment of occupational exposures is a crucial factor in evaluating dose-response relationships and most studies conducted by the Branch have an extensive exposure assessment component. Major assessment efforts in cohort studies have involved exposures to organic solvents, pesticides, benzene, toluene, and diesel exhaust fumes. In the case-control design, jobs have been evaluated for a wide variety of exposures, including chlorinated hydrocarbons and other solvents, arsenic, asbestos, formaldehyde, electromagnetic fields, physical activity, nitrosamines, polycyclic aromatic hydrocarbons, polychlorinated biphenyls, wood dust, gasoline and diesel exhaust, and pesticides. These exposures have been evaluated in studies of cancer of the stomach, nasopharynx, kidney, esophagus, lung, larynx, pancreas, brain, bladder, and lymphatic and hematopoietic system and for studies of parental occupation and childhood cancers. Methodologic studies are also conducted to improve exposure assessment techniques and to understand exposure patterns. A study has been initiated evaluating assessments made from detailed occupational questionnaires with air measurements. The importance of assessing dermal exposure in epidemiologic studies is being described in a manuscript underway. Comparison of jobs identified on death certificates is being made with work history records. In addition, a report describing how exposures to pesticides are being assessed in a large cohort study of pesticide appicators was developed. Two computer programs to assist in exposure assessment for cohort and for case-control studies are being developed. A report describing the exposure assessment procedures for evaluating EMF exposures in a brain cancer case-control study is underway. Reports describing the occurrences of pesticides, chlorinated solvents, wood dust, nitrosoamines and diesel exhaust fumes are being prepared. Detailed questionnaires have been developed for two case-control studies: a kidney cancer study in the US and a bladder cancer study in New England.